Single human fingertip mechanoreceptive afferents simultaneously encode multidimensional aspects of touch

Touch using the hands is essential for recognizing surface features and manipulating objects, where different aspects are encoded by four main types of low-threshold mechanoreceptors (LTMs) in glabrous skin. Although factors such as movement, vibration, and pressure are often studied individually, touch requires their integration to produce complex sensations. We investigated these processes jointly by recording single-unit activity via microneurography from human LTM afferents in the median nerve as periodic gratings slid across their receptive fields, varying the normal force and sliding velocity per trial. Mixed-effects models revealed that fast-adapting type 1 (FA-1) afferent firing was influenced by all three parameters--force, velocity, and spatial period. Slowly-adapting type 1 (SA-1) afferent firing was primarily driven by force, and to a lesser extent, velocity. These findings support the view that FA-1 afferents encode stimulus intensity in an approximately linear manner, while SA-1 afferents function mainly as force detectors, demonstrating that mechanoreceptive afferents provide a complementary and multidimensional representation of texture during sliding contact. This distributed encoding challenges the notion that LTMs are dedicated to single stimulus features, suggesting that tactile information is represented across LTM populations where each class contributes differently-weighted inputs to capture skin-object interactions.